1. Field of the Invention
The present invention relates to a syringe and in particular to a syringe having a piston head which is made of a resin.
2. Related Art
As is well known, prior art syringe mainly comprises a cylinder which accommodates liquid such as drug and a piston which is reciprocally disposed within the cylinder. The piston comprises a piston main body and a piston head (gasket) which is secured to a front end of the piston main body by means of screwing and the like so that it slides along the inner wall of the cylinder while keeping the sealing condition therewith.
Recently, it is known that the cylinder is preferably made of any of cycloolefin resins in view of chemical resistance and heat resistance. On the other hand, the piston head is made of an elastomer such as butyl rubber since it should slide on and along the inner wall of the cylinder while keeping the liquid-tightness therewith.
However, such an elastomer requires a complicated and tedious washing step since plasticizers, cross-linking agents and pigments which are used with the elastomer may be dissolved to the chemical which is contained in the cylinder.
The elastomer (particularly, butyl rubber) has a low sliding ability for the inner surface of the cylinder. In order to make the reciprocal movement of the piston smoother, the inner face of the cylinder is coated with a lubricating agent such as silicone oil.
There is also a problem that it is hard to provide a high stability in size for the reason of the manufacturing process when the piston head is made of an elastomer.
Therefore, it is a main object of the present invention to achieve the simplification of the manufacturing process by omitting the washing step while satisfying the characteristics which are basically required for the syringe, to enable smooth sliding without using any lubricant, to enhance the dimension accuracy and stability and to achieve the reduction in cost by achieving the foregoing.
In view of the above-mentioned object, the present inventors have believed that the piston head is also made of a resin similarly to the cylinder to omit the washing step and to enhance the dimension accuracy and stability and have made efforts to study the manufacturing of the syringe. We have found from our study that if the prior art piston head is made of only a resin, there occur problems in liquid-tightness, sliding characteristics and ability of incorporation of the piston head into the cylinder. We have further made efforts on the research and development of the syringe to solve these latter problems together and made the present invention.
One embodiment of the invention resides in a syringe comprising a cylinder for containing liquid therein and a piston which is reciprocally disposed within the cylinder. The piston including a piston main body and a piston head made of a resin which is secured to a front end of the piston main body and slides along the inner wall of the cylinder while keeping the liquid-tightness therewith. The piston head is formed on the periphery thereof with collar means which contacts with the inner wall of the cylinder, at least the peripheral edge of the collar means being thin walled. The collar means being slidable on and along the inner wall of the cylinder while keeping the liquid-tightness.
An aspect of the invention resides in the collar means comprises collars which are spaced in a direction of sliding of the piston. The collar of at least two adjacent collars, which is on the front side in the sliding direction being supported by the collar which is in the rear side in the sliding direction when the piston slides.
Another aspect of the invention resides in the syringe having a collar means having a base end portion which is thick walled excepting for the peripheral edge.
Another embodiment of the invention resides in a syringe comprising a cylinder for containing liquid therein and a piston which is reciprocally disposed within the cylinder. The piston including a piston main body and a piston head made of a resin which is secured to a front end of the piston main body and slides along the inner wall of the cylinder while keeping the liquid-tightness therewith. The piston head is formed on the periphery thereof with collar groups, each comprising two collars which are close to each other, at least the peripheral edge of each of the collars being thin walled. The collars being slidable on and along the inner wall of the cylinder while keeping the liquid-tightness. The front collar of the collar group having a diameter which is larger than that of the rear collar. The front collar having a larger diameter being supported by the rear collar when the piston is inserted into the cylinder.
Still another embodiment of the invention resides in a syringe comprising a cylinder for containing liquid therein and a piston which is reciprocally disposed within the cylinder. The piston including a piston main body and a piston head made of a resin which is secured to a front end of the piston main body and slides along the inner wall of the cylinder while keeping the liquid-tightness therewith. The piston head is formed on the periphery thereof with collar groups, each comprising three collars which are close to each other, at least the peripheral edge of each of the collars being thin walled. The collars being slidable on and along the inner wall of the cylinder while keeping the liquid-tightness. The intermediate collar of the collar group having a diameter which is larger than that of the front and rear collars. The intermediate collar having a larger diameter being supported by the front and rear collars when the piston is slided in the cylinder.
Yet another embodiment of the invention resides in a syringe comprising a cylinder for containing liquid therein and a piston which is reciprocally disposed within the cylinder. The piston including a piston main body and a piston head made of a resin which is secured to a front end of the piston main body and slides along the inner wall of the cylinder while keeping the liquid-tightness therewith. The piston head is formed on the periphery thereof with at least two collar groups being spaced in a direction of sliding of the piston, each group comprising collars which are close to each other, at least the peripheral edge of each of the collars being thin walled. The collars being slidable on and along the inner wall of the cylinder while keeping the liquid-tightness. The collar group at the distal end comprises two collars. The front collar of the frontmost collar group having a diameter which is larger than that of the rear collar. The front collar having a larger diameter being supported by the rear collar when the piston is inserted into the cylinder. The collar group which is at the rear of the frontmost collar group comprises three collars, the intermediate collar having a diameter which is larger than those of the front and rear collars. The intermediate collar having a larger diameter being supported by the front or rear collar at least when the piston slides, wherein a piston support collar which is thick walled at the base end thereof excepting for the peripheral edge thereof is provided at the rear of these collar groups in a spaced relationship therewith.
An aspect of the invention resides the piston head being formed of a resin which is selected from the group consisting of polypropylene, polyethylene, fluorine, cyclopolyolefin, and polycarbonate resins.